You may not have seen enough good repos. The following is an example commit from freebsd
https://cgit.freebsd.org/src/commit/?id=ac5ff2813027c385f903...
A proper email is like an email. You have the first line as the subject and it may be enough to explain the intent of the diff. But sometimes it’s not enough and you add more details in the body. I strongly believe that people who write the WHAT again don’t know that there’s a diff attached to the commit and think of them a separatete objects. GitHub and VSCode do not really help in that regard.